<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
        <style>
            div#box {
                text-align: center;
            }
            div#box div#btn {
                margin: auto;
                width: 50px;
                height: 50px;
                line-height: 50px;
                background-color: #ddd;
                border-radius: 100%;
                color: #fff;
                cursor: pointer;
            }
        </style>
</head>
<body>
    <div id="box">
        <div id="btn">开</div>
        <img id="img" src="pic_bulboff.gif" alt="" />
    </div>
    <script>
        (function(){
            var btn = document.querySelector("#btn");
            var img = document.querySelector("#img");
            btn.onclick = function() {
                console.log("this:", this);
                //console.log(this.innerHTML);
                if(this.innerHTML == "开") {
                    img.src = "pic_bulbon.gif";
                    this.innerHTML = "关";
                    this.style.backgroundColor = "green";
                } else {
                    img.src = "pic_bulboff.gif";
                    this.innerHTML = "开";
                    this.style.backgroundColor = "#ddd";
                }
            }
        }());
    </script>
</body>
</html>